P077B
DTC P077B
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.
DTC Descriptor
DTC P077B
- Output Speed Sensor Direction Incorrect
Diagnostic Fault Information
Typical Scan Tool Data
Circuit/System Description
The transmission output shaft speed sensor has 2 internal hall-effect type sensors, and is capable of sensing both speed and direction. The transmission output shaft speed sensor mounts to the A/Trans case assembly and is connected to the control solenoid valve assembly through a wire harness and connector. The sensor faces the front differential drive pinion, w/transfer gear, gear assembly machined teeth surface. The sensor receives 8.3-9.3 volts on the OSS supply voltage circuit from the transmission control module (TCM). As the output shaft rotates, the sensor produces a signal frequency based on the machined surface of the output shaft.
The two sensor elements in the transmission output shaft speed sensor are spaced approximately 1/2 a tooth apart.
* When the vehicle is moving in a forward direction, sensor A detects a particular tooth before sensor B.
* When the vehicle is moving in a reverse direction, sensor B detects a particular tooth before sensor A.
The electronics in the sensor combine the two signals and send a signal with a different pulse width. This signal is interpreted by the TCM for speed and direction and is transmitted through the GMLAN circuits to the engine control module (ECM) and the hybrid powertrain control module. The ECM, hybrid powertrain control module, and TCM compare the OSS signal with hybrid motor speed/direction and the ABS wheel speed sensor signal.
Conditions for Running the DTC
* The OSS speed parameter is less than 50 RPM.
* The drive motor estimated output speed is greater than 50 RPM.
Conditions for Setting the DTC
The hybrid powertrain control module or the transmission control module detects an incorrect OSS direction.
Action Taken When the DTC Sets
Hybrid Powertrain Control Module
The hybrid powertrain control module calculates OSS direction based on drive motor 1 and drive motor 2 direction.
Transmission Control Module
The hybrid powertrain control module 1 and ECM use the ABS wheel speed to calculate vehicle speed.
Conditions for Clearing the DTC
Hybrid Powertrain Control Module
P077B is a Type A DTC.
Transmission Control Module
P077B is a Type A DTC.
Diagnostic Aids
Inspect the output speed sensor, harness, connector and control solenoid valve assembly pins for metallic debris and output shaft machined face for damage or misalignment. Proper torque of the output speed sensor mounting bolt is critical to proper output speed sensor operation. Use a terminal test kit for any test that requires probing the control solenoid valve assembly harness connector or a component harness connector.
Reference Information
Schematic Reference
Automatic Transmission Controls Schematics Electrical Diagrams
Connector End View Reference
Component Connector End Views Hybrid/EV Battery Pack X1
Description and Operation
Electronic Component Description Electronic Component Description
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References Programming and Relearning for scan tool information.
Special Tools
EL 38522 - Variable Signal Generator
Circuit/System Verification
1. Verify that DTCs P0721, P0966, P0967, P0969, P0970, P0971, P0973, P0974, P0976, P0977, P2720, P2721, P2728, P2729, or P2730 are not set.
• If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle.
2. Operate the vehicle at 16-32 km/h (10-20 mph) while observing the Transmission Data OSS Direction parameter on the scan tool. The OSS Direction parameter should match vehicle direction.
• If the OSS parameter corresponds with the vehicle direction and the DTC is set in the hybrid powertrain control module and not the transmission control module, replace the T6 power inverter module.
Circuit/System Testing
Perform the Control Solenoid Valve and Transmission Control Module Assembly Output Shaft Speed Input Test Control Solenoid Valve and Transmission Control Module Assembly Output Shaft Speed Input Test.
Component Testing
Control Solenoid Valve and Transmission Control Module Assembly Output Shaft Speed Input Test Control Solenoid Valve and Transmission Control Module Assembly Output Shaft Speed Input Test
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* Control Module References Programming and Relearning for Drive Motor Generator Power Inverter Module, also called the power inverter module, and Control Solenoid Valve Assembly and Transmission Control Module Assembly replacement, programming, and setup.
* Perform the Reset Transmission Adapts Programming and Relearning following all transmission related repairs.